Process for polymerizing ethylene



Patented June 5, 1945 uNlrEo STATE raocass ronrotmmzmc. Ermaua- WilllamEdward Hanford and John-Richard Ro-r -land, Wilmington, DeL, and Howardfiargent 1 Young. Fairville. Pa., assignors to E. I'. du'Pont de Nemours& Company, Wilmington-Bal a corporation of Delaware No. Drawing.

Application February 18, Serial. No. 431,380

lsoi mis. (c1. zea -94) This invention relates to polymerizationprocesses and more specifically to a new and im-- proved processforthe'polymerlzation of ethylene.

The utilization of ethylene as a polymerforming chemical is extremelyattractive commercially and as a consequence its polymerization has beenthe object of a large numberof investigations; Most of theseinvestigations have involved the use of a silent electric discharge orof metal halides, or organic compounds yielding free radicals under thereaction conditions as catalysts as described, for example, in TheChemistry of Synthetic Resins by Carleton Ellis. Generally, how-' ever,the products obtained by these prior art processes have beenoils or softgreases. 4 1

One process which has been an exception to thev prior art, in givingsolid or semi-solid end products 'is that described in U. S. Patent2,153,553, wherein ethylene-is heated to between 100 to 400 C. underpressures of from 50.0 atmospheres upwards, preferably in the presenceof oxygen to catalyze The above and (other objects of the present in.vention are accomplished by heating substantially oxygen-free ethylenein the presence of a normally liquid non-polymerizable organic medium incontact with an organolithium compound and in the absence 'ofhydrogenatlng catalysts.

In the practiceqof this invention. any organolithium compound can beused as a catalvst, although the preferred classes are the alkyllithiumsand thearylilthiums, such'as methvllithium, n? butyllithium,isoamyllithium, octyllithium. dodecyllithium, phenyllithium, andbenzyllithium.

tion of these diethyl ether may be used 'as a solvent. j

The concentration of catalyst required in the practice of this invention"can vary over a wide range. For reasons of economy and in order toobtain products of the best molecular weight, however. it isgenerallydesirable to use low concentrations of catalyst, for example, from about0.01 to about 1%. Lower molecular weight products may be desirable formany-uses, and these are conveniently prepared with catalystconcentrations up to 15% or more, based on the amount of polymerizablemonomer. I

As solvents for use in this invention, nonpolymerizable normally liquidorganic compounds are suitable. It is generally preferable to use sat-These are conveniently prepared by the method of Ziegler and Colonius(Ann. 4'79, 135 (1930)) though any other method can be used. In themethod of Ziegler and Colonius the organolithium compound is prepared bythe reaction of an appropriatechloro or bromo hydrocarbon with ahydrocarbon suspension of clean lithium metal. The reaction betweenorganic halides and lithium proceeds best if carried out at a slightlyelevated temperature underan atmosphereof inert gas. Certainorganolithium compounds, such as phenyllithium, do not show 'a high rateof reaction with oxygenated solvents, and for the preparauratedaliphatic and aromatic hydrocarbons such as benzene, isooctane, toluene,petroleum ether, and the like. Many oxygenated solvents react withalkyllithiums. Aryllithiums, however, show lower reactivity withoxygenated solvents, and with these it is convenient to use a solventsuch as diethyl ether.

The most critical feature of this invention is the purity of theethylene employed and particularly its oxygendcontent. The ethylene maycontain traces of methane. ethane, propane, nitrogen, or hydrogen, orother olefines although the proportions of other olefins should be keptlow since, in general, other olefins tend to lower the softeningpoint ofthe product.

Inasmuch as oxygen is the most critical of the impurities that may beencountered in ethylene, commercial ethylene is not suitable for use inpracticing our invention, containing as it does up to 1500 P. P. M. andmore of oxygen.

Specially purified ethylene containing less'than 1000 P. P. M. of oxygen(0.1%) and preferably less than 500 P. P. M. of oxygen is desirable forthe practice of this invention. Sych a quality. of ethylene may beconveniently prepared by de-- oxygenating commercial ethylene over areduced copper catalyst or by fractional distillation of commercialethylene. By these processes the oxygen content is easily reduced tobetween 10 and 20 P. P. M. and with greater care this can be reduced toless than 5 P. P. M. if desired.

The general effect of increasing the temperature is to accelerate therate of reaction but this increase in reaction rate is accompanied by adecrease in the molecular weight of the polymer. In the practice of thisinvention there can be used temperatures in the range of 25 to 350 C.v

within this range products having the bestcombination of properties areobtained at a practical reaction rate.

The molecular weight of ethylene polymers is a function of the pressureused in their prepara-- pressure above atmospheric may be used in the 1practice of this invention, although itis generally preferred to operatein the range oi from 20 atmospheres to 1500 atmospheres.

In carrying out the invention the. polymerization may be eiIected in abatch, semi-continuous, or in a continuous process. In one method ofcarrying out a batch process, a pressureresistant reaction vessel ischarged with a-su spension or solution of the organolithium compound,for example, a benzene solution of n-butyllithium. Since the. success ofthis process depends upon rigid exclusion of any substantial amount ofmolecular oxygen, this charging operation is most suitably effected byuseof a separate loadin'g'vessel which canbe filled with the solution oforganolithium compound in vac-J uum or under an inert gas such aspurified nitrogen. In one convenient form the loading vessel andpressure reaction vessel are provided with ground joints which arefitted'together through a T. The pressure reaction vessel is evacuatedthrough theT, the latter closed and a cock to the charging vessel openedto admit a measured amount of solution to the-reaction vessel. The valveon the reaction vessel is then closed, thecharging vessel removed, andthe reaction vessel placed in a heated shaker machine. The-vessel isthen connected to a sourceof high pressure ethylene, Stted'withrecording and controlling thermocouples; the valve is opened, ethylenesubstantially free of oxygen is admitted to the pressure desired andheating and agitation are started. Reaction starts immediately uponreaching the reaction temperature or even spontaneously if highconcentrations ofcatalyst are employed. When reaction is complete,

. of hard, waxy polymer.

Various changes may be made in the details and preferred embodiments 01this invention or sacrificing anyas evidenced by lack of furtherpressure drop,

- the vessel. is cooled, bled of excess ethylene,

opened and the contents discharged. The product is isolated by simpledistillation or-by steam distillation of the solvent, followed bydrying.

The following examples illustrate in detail the practice of thisinvention and demonstrate operable conditions. unless otherwisespecified; I

Example 1 A stainless steel-lined vessel is charged with.

8.8 parts of n-butyllithium in 250 parts by volume of benzene. Thevessel is closed, placed in a shaker machine and pressured with ethyleneas described above. During a reaction time of about P. P. M. of oxygen.The excellent quality of this polymer, along. with. its ease of isola--viscosity characteristics as the tion. illustrates the advantages ofthis invention. I

smmple 2: A stainless steel-lined. reaction vessel contains ing 10 partsof phenyllithium in 150 parts by volume of ether is charged withethylene as described in Example 1. In a reaction time of 16.5 hours at56 to 73 C. and 405 to 950 atmospheres ethylene pressure. the totalobserved pressure drop is 420 atmospheres. The product, isolated asbefore, amounts to 100 parts oi a hard wax. This product has the sameintrinsic product of Example 1.

Example 3 I Followingthe operative details of Example 1, a stainlesssteel-linedyessel is charged with 4.3 parts of n-butyllithium in 100parts by volume of benzene. In a reaction timeof 17 hours at 20 to 26 C.and 905 to 970 atmospheres ethylene pressure, there is an observedpressure drop of about atmospheres. This reaction yields 4.5partsof ahard, waxy, polymer which has an intrinsic viscosity of 0.63 (0.25% inxylene at C.) and which melts at to 121 C.

' V E's-ample 4 In a manner such as described in Example 1, asilver-lined reaction vessel is charged with 0.4 part of n-butyllithiumin 250 parts by volume of isooctane. In a reaction time of 17.75 hoursat 98 to 100 C. and 755 to 990 atmospheres ethylenej pressure, theobserved'pressure drop totals 555 atmospheres. This reacti n yields 30parts without departing therefrom of the advantages thereof.

We claim: 1. In a process for producing mers which comprises heatingethylene in a nonpolymerizable organic liquid medium, in the presence ofa material selected-from the group consisting of alkyl and aryllithiumcompounds as the sole catalyst, the step Miichpomprises car- Parts givenare by weight rying out the process with ethylene containing less than1000 parts per million of oxygen.

2. In a process for producing ethylene polymers which comprises heatingethylene in a non-polymerizable organic liquid medium, in the presenceof from 0.01 to 15% of a material selected from the group consisting ofalkyl and aryl lithium compounds'as the sole catalyst, the step whichcomprises carrying out the process I with ethylene containing less than1000 parts per million of oxygen.

' 3. In a process for producing ethylene polymers which comprisesheating ethylene in a nonpolymerizable organic liquid medium, in thepresence of from 0.1 to 1% of a material selected from the groupconsisting of alkyl and aryl lithium compounds as the' sole catalyst,the step which comprises carrying out the process with ethylenecontaining less than 1000 parts per million of oxygen.

4. In a process for producing ethylene polymers which comprises heatingethylene in benzene, in the presence of a material selected from thegroup consisting of alkyl and aryl lithium compounds as the solecatalyst, the step which comprises carrying out the process withethylene containing less than 1000 parts per million of oxygen.

ethylene poly- 1000 parts per million ofoxygen.

alkyl and aryl lithium compounds as the sole catalyst, the step whichcomprises carrying out the process with ethylene containing less than1000 parts per million of oxygen. a 6. In a process for producingethylene polymers which comprises heating ethylene in benzene, in thepresence offrom 0.01 to '1% of a ma-.

terial selected from the group consisting of alkyl i 1000 parts ableorganic liquid medium, in the presence of irom 0.01 to of a materialselected .from the group consisting of alkyl and aryl lithium compoundsas the sole catalyst, the step which comprises carrying out the processwith ethylene containing less than 1000 parts per million of oxygen.

12. In a process for producing ethylene polymers which comprises heatingethylene at a temperature of to 350 C., in a non-polymerizable organicliquid medium, in the presence of irom'0'.01 to 1% of a materialselected from the group consisting of alkyl and aryl lithium compoundsas the sole catalyst, the step which comconsisting of alkyl and aryllithium compounds as the sole catalyst, the step which comprisescarrying out the process with ethylene containing less than 500 partsper million of oxygen.

8. In a process for producing ethylene polymers mers which comprisesheating ethylene in ben-' zene, in the presence of a material selectedfrom the group consisting of alkyl and aryl lithium compounds as thesole catalyst,'the step-which comprises carrying out the process withethylene containing less than 500 parts per million of.

oxygen. Y

10. In a process for producing ethylene polymers which comprises heatingethylene at a temperature of 25 to 350 C., in a non-polymerizableorganic liquid medium, in the presence of a material selected from thegroup consisting of alkyl and aryl lithiumcompounds as the solecatalyst, the step which comprises carrying out the process withethylene containing less 11. In a processfcr producing ethylene polymers which comprises heating ethylene at a temperature of 25 to 350 C.',ln anon-polymerizprises carrying out the 'process with ethylenecontaining less than 1000 parts per [million of 13. Ina process for.producing ethylene polymers which comprises, heating ethylene inbenzene, in the presence-ct from 0.01 to 15% of a material selected fromthe group consisting of alkyl and aryl lithium compounds as the solecatalyst, the step which comprises carrying out the process withethylene containing less than 500 parts per'million of oxygen.

.14. In a process for producing ethylene polymers at a temperature of to0., in a nonpolymerizable organic liquid medium,,in the presence of amaterial selected from the group consisting of alkyl and aryl lithiumcompounds as the sole catalyst, the step which comprises carrying outthe process with ethylene containing less than 1000 parts per million ofoxygen. s

15. In a process for producing ethylene poly presence of, a materialselected from the group consisting of alkyl and aryl lithium compoundsas the sole catalyst,'the stepwhich comprises carrying out the processwith ethylene containing less than 1000 parts per million of oxygen.

'as the sole catalyst, the step which comprises carrying out the processwith ethylene containing less than 500 parts per million vof oxygen,

WILLIAM EDWARD HANFORD. JOHN RICHARD ROLAND. a HOWARD SARGENT YOUNG.

